The present invention relates to the treatment of oils in refineries, and more particularly to the treatment of oils containing paraffin or so-called paraffinated oils, for separating the paraffin from the oil and vice versa. These installations may include a system that provides an initial dilution of the oil to be treated, hereinafter called charge oil, with appropiate solvents, in usual cases with "MEK" (methylethyl ketone) and toluol, respectively, in proportions, for example, of 60% and 40% respectively.
According to this usual process, the charge oil must be subjected, for the required separation of the paraffin from the oil, to cooling that is done in known type heat exchangers in which a refrigerant liquid delivers cold to the charge oil, to cool it for the purpose of the required separation.
For example, for an oil of the "LUB O" type, the temperature is typically carried down to about -28.degree. C. In these installations, as is known to the experts in this field, one refrigerant fluid is generally the recovery oil stemming from the treatment of the charge oil, that is to say the oil that has already been passed through the cooling and filtration process, and this permits the use of the cold already given off to the recovery oil by previous removal of paraffin and removal of oil.
Such refrigerators are usually called "chillers" in these installations, but in reality the refrigeration installation is more complex and includes pre-refrigerators, so-called "prechillers", that are located upstream of the refrigerators or "chillers".
The heat exchanger section mentioned above and relating to said "prechillers" (generally there are two of them: a prechiller I and a prechiller II) contains for a good operation of the installation, a series of restrictions or valves along the charge oil line and branches of same to the "prechillers", and likewise along the oil recovery line and the respective branches of same to the "prechillers" for transfer of cold to the charge oil.
Generally, for each prechiller there are three restrictions or valves on each flow, respectively one on the line toward the outlet and return of the branch and two in the "chiller" branch, respectively upstream and downstream of same.
The installation is adjustable, by means of these valves for good functioning but, as is known the process is not always constant for various reasons and also because of the diversity of the components of the charge oil, in which the content in paraffin is not always constant.
In these installations, the recovery oil temperature at the output of the prechillers is generally at -20.degree. C. and, hence, it is for this reason that it is used as an exchanger fluid for the recovery of cold.
However, because of the inconstancy of the characteristics of the charge oil and other known factors of the technology, for example variation of the ambient temperature, functional problems, etc., it is noted that the charge oil becomes either too cooled or arrives in too little quantity to the prechillers, so that the process becomes inconstant and difficult to normalize.
However, the most serious disadvantage is noted when the charge oil is cooled excessively, increasing the viscosity, obstructing the conduits and blocking the system. Then it is necessary to intervene manually with the recovery oil refrigerating valves, opening the line restrictions, adjusting the flow of the prechillers, and this manually, in order to increase the temperature of the charge oil. In cases of total obstruction, the work is much more complex, requiring increasing the percentage of solvent in the charge oil to increase its fluidity and blocking the flow of refrigerant oil and/or providing for direct washing, with solvent, of the charge oil tubing running to the prechillers, which obviously includes stopping production and consequent reduction in output of the installation.